1. Field of the Invention
The invention relates to in-situ measurement of steam or gas turbine blade tip gap between rotating blades and the circumscribing turbine casing ring segment. More particularly, embodiments of the invention relate to in-situ blade tip gap measurement by mounting a radially oriented displacement sensor directly on a turbine blade while in-situ within an industrial gas turbine and rotating the rotor so that the blade sweeps at least a portion of the circumscribing turbine casing ring segment in either the compressor or hot gas turbine sections. In other embodiments of the invention the entire circumference of the circumscribing casing ring segment is swept by rotating the rotor while the industrial gas turbine is operated in turning gear mode.
2. Description of the Prior Art
During assembly and at periodic times throughout the life of a gas turbine blade tip clearances must be measured. Proper tip clearance enables better efficacy of gas turbines and lowers harmful emissions. To date there are ways of measuring tip clearances, but the methods requiring the removal of the upper casing that circumscribes the turbine blade tips during measurement, limited number of inspection points, or take a relatively long time to complete.
There are typically two known common methods for measuring blade tip clearances. In the first method the measurement of tip clearance is typically accomplished by removing the turbine or compressor case upper half to provide access to the blades. Shims are then inserted between the blades tips and the flow path side or ring segments of the lower case at the horizontal joint. Measurements are typically taken at the leading and trailing edge sides of the blade tips for every blade. These measurements are referred to as half shell measurements. This method provides very little accuracy or reproducibility because the lower case tends to change shape without the upper case in place. Also, the half shell measurement locations are not necessarily representative of the local case shape at all angular rotational positions about the entire rotational surface swept by the turbine blade.
The second known common method for measuring blade tip clearances is by opening an inspection port in the side of the engine that is aligned with the blade path. A contact or non-contact probe is inserted into the port to measure the distance of the blade tip from the gas path side of the case or ring segments. There are a limited number of these inspection ports oriented about the turbine casing. Therefore only data from select rows and cord positions can be obtained. Furthermore, as noted above in the description of the first known inspection method the inspection locations may not be representative of the casing shape about the entire rotational circumference of the turbine. In some spots, due to casing shape disparities, there may be varying tip gap.
Thus, a need exists for a method to measure turbine blade tip clearances in-situ within an assembled turbine without removing part of the turbine casing that circumscribes the blade tips.
A need also exists for a method to measure turbine blade tip clearances in-situ within an assembled turbine casing, so that localized blade tip gap differences can be identified and measured.
An additional need exists for a method to determine whether the turbine rotor assembly is aligned within its circumscribing turbine casing, so that alignment can be adjusted to assure rotor rotational axis concentricity within the casing. For example, so that turbine vane carriers are centered to the rotor during alignment verification.